Ruthenium(II) complexes of multidentate ligands derived from Di(2-pyridyl)methane

Article abstract of DOI:10.1071/CH03019

Bis(2,2′-bipyridyl)ruthenium complexes of the model ligand di(2-pyridyl)methane (1) and its multidentate derivatives 1,1,2,2-tetra(2-pyridyl)ethane (2), tetra(2-pyridyl)ethene (3), and hexa(2-pyridyl)[3]radialene (4) have been prepared and characterized by NMR, visible absorption spectroscopy, electrochemical measurements, and, in two cases, by X-ray crystallography. Complexes of (2) and (3) exist as conformationally rigid species with lower than expected symmetry. Ligands (2) and (3) proved surprisingly resistant to forming dinuclear ruthenium complexes. The two diastereoisomeric dinuclear complexes of (4), ΔΛ/ΛΔ and ΔΔ/ΛΛ (rac), are shown to be locked in conformations of C₁ and C₂ point-group symmetry, respectively. This represents a rare example where the ΔΛ/ΛΔ-dinuclear complex of a achiral, symmetrically bridging ligand is not a meso compound.

Full text of DOI:10.1071/CH03019

Full Papers
CSIRO PUBLISHING
www.publish.csiro.au/journals/ajc
Aust. J. Chem. 2003, 56, 657–664
Ruthenium(ii) Complexes of Multidentate Ligands Derived from
Di(2-pyridyl)methane
Deanna M. D’Alessandro,A F. Richard Keene,A,C Peter J. SteelB,C and Christopher J. SumbyB
A School of Pharmacy and Molecular Sciences, James Cook University, Townsville 4811, Australia.
B Department of Chemistry, University of Canterbury, Private Bag 4800, Christchurch, New Zealand.
C Authors to whom correspondence should be addressed (e-mail: p.steel@chem.canterbury.ac.nz,
richard.keene@jcu.edu.au).
Bis(2,2ꢀ-bipyridyl)ruthenium complexes of the model ligand di(2-pyridyl)methane (1) and its multidentate deriva-
tives 1,1,2,2-tetra(2-pyridyl)ethane (2), tetra(2-pyridyl)ethene (3), and hexa(2-pyridyl)[3]radialene (4) have been
prepared and characterized by NMR, visible absorption spectroscopy, electrochemical measurements, and, in two
cases, by X-ray crystallography. Complexes of (2) and (3) exist as conformationally rigid species with lower than
expected symmetry. Ligands (2) and (3) proved surprisingly resistant to forming dinuclear ruthenium complexes.
The two diastereoisomeric dinuclear complexes of (4), ꢀꢁ/ꢁꢀ and ꢀꢀ/ꢁꢁ (rac), are shown to be locked
in conformations of C1 and C2 point-group symmetry, respectively. This represents a rare example where the
ꢀꢁ/ꢁꢀ-dinuclear complex of a achiral, symmetrically bridging ligand is not a meso compound.
Manuscript received: 28 January 2003.
Final version: 4 March 2003.
Introduction
ring.[7] The simplest of these is that in which a methylene
group (X = CH2) acts as the spacer. This compound, di(2-
pyridyl)methane, has been sparingly used as a ligand.[8,9]
The methylene spacer has the effect of insulating the two
rings from one another, thereby removing any conjugation
between the two heterocyclic rings. Surprisingly, however,
bridging ligands that contain two or more such subunits have
been virtually ignored. We now describe three such ligands
and efforts to prepare their dinuclear ruthenium complexes.
2,2ꢀ-Bipyridine (bpy) (Diagram 1) has been used for over
a century[1] as the classical chelating bidentate ligand, and
has been shown to form stable complexes with almost all
metals in the periodic table.[2] In recent years, many new
ligands have been synthesized that contain two, or more,
bpy subunits and which act as bridging ligands for the for-
mation of dinuclear, or multinuclear, metal complexes.[3]
Ruthenium(ii) complexes of such ligands have been partic-
ularly well studied, with much work having been directed at
their stereochemical,[4] electrochemical, and photophysical
properties.[5] Particular emphasis has been placed on ligands
that facilitate strong metal–metal interactions.[5,6]
Results and Discussion
Ligand Syntheses
Ligands such as bpy coordinate to metals with the forma-
tion of a stable five-membered chelate ring. Much less studied
are the class of ligands shown in Diagram 1 that contain two
2-pyridyl substituents separated by a single atom spacer (X),
and which result in the formation of a six-membered chelate
The key synthetic intermediate and model ligand, di(2-
pyridyl)methane (1) (Scheme 1), can be readily prepared
in high yield from di(2-pyridyl)ketone, by Wolff–Kishner
reduction, as reported by Canty and Minchin.[8] This was
converted to the potentially bridging ligand 1,1,2,2-tetra(2-
pyridyl)ethane (2), by an adaptation of the method of Canty[8]
in which (1) was deprotonated and treated with a suitable
oxidant. We preferred to use iodine instead of mercuric
iodide as the oxidant, as this gave more consistent and repro-
ducible results and avoided the production of mercury as a
by-product.
R
R
X
N
N
N
N
The new ligand tetra(2-pyridyl)ethene (3), was prepared
by two methods. In the first method, (2) was oxidized
with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) in
refluxing toluene. This gave (3) in low yield and led to sub-
sequent purification difficulties. In a preferred procedure,
bpy
R ꢀ H
X ꢀ O, S, NH, CO, CH2
Me2bpy R ꢀ Me
Diagram 1.
© CSIRO 2003
10.1071/CH03019
0004-9425/03/070657

658
P. J. Steel et al.
(3) was prepared by the dehydration of 1,1,2,2-tetra(2-
pyridyl)ethanol (5), a product of the aerial autooxidation
of di(2-pyridyl)methane. Treatment of (5) with thionyl chlo-
ride and pyridine at room temperature gave the alkene (3) in
high yield. Hexa(2-pyridyl)[3]radialene (4) was prepared by
reaction of (1) with tetrachlorocyclopropene, as previously
described.[10]
and only the mononuclear complexes [Ru(bpy)2(3)](PF6)2
(10) and [Ru(Me2bpy)2(3)](PF6)2 (11) were formed by
conventional synthetic techniques.
More aggressive conditions were employed in attempts
to prepare dinuclear ruthenium complexes of (3). By heat-
ing a suspension of [Ru(bpy)2Cl2] and (3) in ethylene glycol
in a modified microwave oven on high power for 45 min,
a red-brown solution was obtained. This contained three
components that were separated chromatographically, using
a column of SP Sepharose Fast Flow cation exchanger and
a gradient elution procedure using aqueous 0.1–0.5 mol L−1
NaCl as the eluent. Disappointingly, the three compo-
nents were identified by NMR as unreacted [Ru(bpy)2Cl2],
mononuclear complex (10), and an unsymmetrical mononu-
clear ruthenium complex containing an unidentified decom-
position product of (3).
However, the analogous microwave-assisted reaction of
[Ru(bpy)2Cl2] with (4) in ethylene glycol produced a green-
brown solution that was separated into the mononuclear and
dinuclear products via a gradient elution procedure using
aqueous 0.1–0.5 mol L−1 NaCl as the eluent. Four bands were
eluted: Band 1 (light red, 0.2 mol L−1 NaCl), Band 2 (purple,
0.3 mol L−1 NaCl), Band 3 (green, 0.4 mol L−1 NaCl), and
Band 4 (green, 0.4 mol. L−1 NaCl). These were identified
by a combination of electrospray mass spectrometry (ESMS)
and 1- and 2-D NMR techniques. Band 1 was identified by
ESMS as a mixture of [Ru(bpy)2(L)]2+ complexes, where
L = di(2-pyridyl)ketone and its ethylene acetal. Band 2 was
unreacted [Ru(bpy)2Cl2]. Bands 3 and 4 were identified by
ESMS and NMR (see below) as the two diastereoisomeric
forms of [{Ru(bpy)2}2(µ-(4))](PF6)4.
1
The H NMR spectra of these four highly symmetrical
ligands, in both deuterated chloroform and acetonitrile, were
readily assigned on the basis of the characteristic chemi-
cal shifts and spin–spin coupling patterns of 2-substituted
pyridines. The chemical shifts for the new ligand (3) in chlo-
roform are listed in the Experimental section and those given
for (1)–(4) in acetonitrile are included in Table 1. The chem-
ical shifts for (4), which adopts a propeller conformation
in solution,[10] are at unusually high field positions due to
through-space shielding by adjacent pyridine rings.
Preparation of Ruthenium Complexes
Treatment of [Ru(bpy)2Cl2], or [Ru(Me2bpy)2Cl2], with
(1) in ethanol/water gave the expected mononuclear com-
plexes [Ru(bpy)2(1)](PF6)2 (6) and [Ru(Me2bpy)2(1)](PF6)2
(7) (Scheme 1), which were characterized by elemental
analysis, mass spectrometry, and 1H NMR spectroscopy.
Compound (6) has previously been reported as part of a
study of the photochemistry of related complexes.[11] Reac-
tion of (2), a potentially ditopic doubly bidentate ligand,
with either ruthenium precursor unexpectedly yielded only
the mononuclear complexes [Ru(bpy)2(2)](PF6)2 (8) and
[Ru(Me2bpy)2(2)](PF6)2 (9). Despite repeating these reac-
tions several times with substantial excesses of the ruthenium
precursors, and a number of variations in method and reaction
time, the formation of dinuclear products was not detected.A
dinuclear palladium complex of this ligand has been reported
previously.[8,12] Similar observations were made for (3),
which again has the potential to bridge two metal atoms,
NMR Spectra of the Ruthenium Complexes
The 1H NMR chemical shifts for the ligands (1)–(4)
and their ruthenium complexes (6)–(13) are given in
Table 1, along with the coordination-induced shift values
2+
2+
(i) BunLi
N
N
N
N
N
N
N
N
[RuL2Cl2]
[RuL2Cl2]
RuL2
(ii) I2
N
N
N
N
Ru
L2
(1)
(6) L ꢀ bpy
(7) L ꢀ Me2bpy
(2)
(8) L ꢀ bpy
(9) L ꢀ Me2bpy
Ref. [10]
[O]
DDQ
N
N
2+
N
N
N
N
N
N
N
N
N
N
SOCl2
[RuL2Cl2]
N
N
OH
N
RuL2
pyridine
N
N
N
(4)
(5)
(3)
(10) L ꢀ bpy
(11) L ꢀ Me2bpy
Scheme 1.

Ruthenium(ii)–Di(2-pyridyl)methane Derived Complexes
659
(CIS = δcomplex − δligand) in italics. The assignments were
made on the basis of spin–spin coupling information, 2-D
COSY, 1-D TOCSY, and 1-D NOESY experiments.
ruthenium. This is exemplified by the range of CIS values
that are found for complexes (6)–(13). We have previously
identified a number of factors that influence the sign and
magnitude of the CIS values that are observed when a
ligand coordinates to a ruthenium atom.[13] These include
ligand-to-metalσ-donation, metal-to-ligandπ-backdonation,
chelation-imposed conformational changes, disruption of
the inter-ring conjugation, and inter-ligand through-space
ring-anisotropy effects.
Dramatic changes in the 1H NMR chemical shifts
are sometimes observed when a ligand is coordinated to
Table 1. Chemical shifts and CIS values for ligands (1)–(4) and
complexes (6)–(13)
Compound
H3
H4
H5
H6
CH(2)
In the model mononuclear complexes (6) and (7)
the six-membered chelate ring of the coordinated di(2-
pyridyl)methane is expected to exist in a boat conformation.
This reduces the symmetry of the complex and would result
in separate signals for the diastereotopic protons of the CH2
group and all pyridine rings, unless there were rapid intercon-
version of the two boat conformers on the NMR timescale. In
these two complexes such interconversions are indeed rapid,
as indicated by the CH2 protons appearing as sharp singlets in
the 1H NMR spectra.The CIS values (Table 1) for the protons
of (6) and (7) are very similar, as expected for the subtle dif-
ferences of the auxiliary bpy ligands. The large negative CIS
values for the H6 protons result from inter-ligand through-
space ring-anisotropy effects, because on complexation these
protons lie over the shielding plane of adjacent bpy rings.The
other CIS values for these complexes are comparable with
other previously reported values.[6,13]
(1)
(6)
CIS
(7)
CIS
7.33
7.71
0.38
7.69
0.36
7.71
7.90
0.19
7.88
0.17
7.22
7.14
8.53
7.58
4.32
4.61
0.29
4.60
0.28
−0.08
−0.95
7.13
7.60
−0.09
7.05
7.20
0.15
6.97
−0.93
8.39
8.59
0.20
7.88
(2)
(8)
CIS
(8)
CIS
(8)
CIS
(8)
CIS
(9)
CIS
(9)
CIS
(9)
7.51
7.81
0.30
7.54
7.83
0.29
7.54
0
7.72
0.18
7.54
0
5.76
5.90
0.14
6.71
0.95
7.32
−0.19
−0.08
−0.51
7.67
7.12
7.91
0.16
7.47
0.07
6.75
−0.48
7.13
−0.04
−0.30
−1.26
7.82
7.82
0.28
7.53
−0.01
7.68
0.14
7.52
−0.02
7.21
8.59
5.89
0.13
6.67
0.91
0.31
7.28
0.16
6.98
0.20
7.89
−0.23
−0.07
−0.50
7.65
7.10
7.91
The 1H NMR spectra of the mononuclear ruthenium com-
plexes (8) and (9) are somewhat more complicated because
the two boat conformations of the six-membered chelate ring
are very different. Since the conformer with the CH proton
in the flagpole position and the rest of the non-coordinated
portion of the ligand in the bowsprit position is much more
stable than the other conformer, this complex is locked in one
conformation, which has C1 symmetry. As a consequence all
eight pyridine rings are non-equivalent and were identified
by 2-D COSY and 1-D TOCSY experiments. The CIS values
experienced by ligand (2) upon coordination to ruthenium
range from −1.27 to +0.95 ppm (Table 1).
CIS
(9)
CIS
0.14
7.46
−0.05
0.05
6.74
−0.31
7.17
7.17
0.00
7.39
0.22
6.88
−0.48
7.12
−1.27
(3)
7.05
5.56
−1.49
8.32
1.27
7.35
0.3
7.31
0.26
5.31
−1.74
8.34
1.29
7.30
0.25
7.30
0.25
7.54
7.30
8.45
8.52
0.07
8.46
0.01
7.19
−1.26
8.04
−0.41
8.56
0.11
8.45
0
7.19
−1.26
8.02
−0.43
8.16
7.74
(10)
CIS
(10)
CIS
(10)
CIS
(10)
CIS
(11)
CIS
(11)
CIS
(11)
CIS
(11)
CIS
−0.24
7.97
0.43
7.52
−0.02
−0.29
7.55
7.16
0.01
7.30
−0.01
7.18
0.01
7.39
0.22
−0.24
7.97
Complexes (10) and (11) also have C1 symmetry due to
a restricted conformation of the six-membered chelate ring
0.43
7.48
6,87
1
of the coordinated ligand. Interestingly, the H NMR spec-
−0.06
−0.30
trum for (10) reveals that one H3 proton lies in a strongly
shielded environment (5.56 ppm, CIS −1.49 ppm), while
a bpy-H6 proton lies in a strongly deshielded environment
(10.43 ppm). On examination of the crystal structure (see
below) and Dreiding models, the former is assigned as the
H3 proton of the non-coordinated ring b of (3) which lies
directly over the shielding region of bpy ring a of the com-
plex (Diagram 2). The resonance at 10.43 ppm is assigned to
7.53
7.15
−0.01
7.16
7.86
0.70
7.46
−0.02
7.15
7.31
0.16
7.25
(4)
6.91
7.44
0.53
7.11
0.20
(12)
CIS
(12)
CIS
(12)
CIS
(12)
CIS
(12)
CIS
(13)
CIS
(13)
CIS
(13)
CIS
−0.52
8.12
0.30
6.37
0.10
6.70
−0.04
7.15
4.93
−1.98
−0.79
−0.45
−1.01
6.54
6.88
7.05
7.84
−0.37
7.00
0.09
−0.28
6.87
−0.10
6.99
−0.32
7.17
−0.29
−0.16
−0.99
4.69
6.27
6.85
7.90
−2.22
−0.92
6.87
−0.30
6.95
−0.26
7.13
6.86
−0.05
7.69
0.78
−0.32
−0.20
−1.03
7.96
7.38
7.92
0.77
0.23
−0.24
Diagram 2.

660
P. J. Steel et al.
the H6 proton of bpy ring a, which lies close to the nitrogen
atom and the deshielding region of the non-coordinated ring
c of (3). This rationale is based on the assumption that the
solid-state and solution-phase structures of complex (10) are
similar. We believe that this is assisted by a stabilizing hydro-
gen bond-type interaction between the nitrogen atom of ring
b and the H3 proton of ring c as is found in the crystal struc-
ture (see below). Such C–H · · · N interactions are now well
recognized as offering significant energetic stabilization.[14]
The CIS values (Table 1) for the ligand (3) in complex (10)
range from −1.49 to +1.27 ppm and, as expected, are similar
to those observed for the Me2bpy complex (11).
(12) ꢁꢂ/ꢂꢁ
(13) ꢁꢁ/ꢂꢂ (rac)
Diagram 3.
ESMS had shown that complexes (12) and (13) were iso-
mers of dinuclear complexes in which the radialene ligand
(4) bridges two Ru(bpy)2 subunits. Normally,[4] the link-
ing of two chiral Ru(bpy)2 moieties by a symmetrical
bridging ligand leads to two diastereoisomers: a ꢀꢁ/ꢁꢀ
(meso) diastereoisomer, with Cs point-group symmetry, and
a ꢀꢀ/ꢁꢁ (rac) isomer, with C2 point-group symmetry.
Surprisingly, however, the 1H NMR of (12) was signifi-
cantly more complicated than that of (13), with complex (12)
displaying 56 unique aromatic proton resonances, whereas
(13) showed only 28 signals. This clearly indicated that
one of the isomers has reduced (i.e. C1) symmetry. Despite
the complexity of both spectra, the individual pyridine ring
spin systems were identified by standard 1- or 2-D NMR
experiments.
The use of Dreiding models of the diastereoisomeric
forms of [{Ru(bpy)2}2(µ-(4))]4+ proved to be of consider-
able assistance in rationalizing the differences observed in the
1H NMR spectra of the diastereoisomeric forms. Assuming
that the [3]radialene core is planar,[10,15] the six-membered
chelate rings are required to adopt boat conformations on
opposite faces of this core, with one boat ‘up’ and the other
‘down’with respect to the plane of the three-membered ring.
All other conformations are excluded on steric grounds. As
a consequence, the ꢀꢁ/ꢁꢀ diastereoisomer (12) possesses
C1 symmetry (lacking the mirror plane of the more common
mesoisomers), whiletheꢀꢀ/ꢁꢁ(rac)isomer(13)possesses
C2 symmetry. The different symmetries of the diastereoiso-
meric forms account for the observation of 56 and 28 proton
signals in the 1H NMR spectra of the ꢀꢁ/ꢁꢀ and ꢀꢀ/ꢁꢁ
diastereoisomers, respectively.
Examination of the Dreiding models also aid in the inter-
pretation of some unusual chemical shifts observed in the
1H NMR spectra. The C1-symmetric (ꢀꢁ/ꢁꢀ) diastereo-
isomer (12) has signals at 4.93 (1 H) and 10.00 ppm (1 H),
whilst the C2-symmetric (ꢀꢀ/ꢁꢁ) isomer (13) has signals
at 4.69 (2 H) and 9.73 ppm (2 H). In the more-symmetrical
ꢀꢀ/ꢁꢁ diastereoisomer (13) the H3 protons of rings e and eꢀꢀ
(Diagram 3) lie directly over the shielding regions of rings b
and b, respectively, of the ancillary bpy ligands and are shifted
upfield, giving rise to the signal at the remarkably high field
position of 4.69 ppm (2 H). In the less-symmetrical ꢀꢁ/ꢁꢀ
isomer (12), the H3 proton of ring j is similarly shielded by
bpy ring b, but the H3 proton of ring e lies in a relatively
less-shielded environment due to the opposite chiralities of
the two metal centres. Thus, the upfield signal at 4.93 ppm
in the ꢀꢁ/ꢁꢀ diastereoisomer is attributed to the single H3
proton of ring j.
A similar rationale accounts for the unusual downfield
signals. Whereas the signal at 9.73 ppm in the ꢀꢀ/ꢁꢁ
diastereoisomer (13) is associated with two H6 protons, the
signal at 10.00 ppm in the ꢀꢁ/ꢁꢀ isomer (12) is attributed
to a single H6 proton. This suggests that the protons must
be associated with the axial pyridine rings of the ancillary
bpy ligands which lie over the bridging ligand (e.g. a or b
rather than c or d). Examination of the Dreiding model for
the ꢀꢀ/ꢁꢁ diastereoisomer (13) reveals that the H6 pro-
tons of rings b and bꢀ lie very close to the nitrogen atoms of
the non-coordinated rings g and gꢀ, respectively, and are thus
strongly deshielded. By contrast, the H6 protons of rings a
and aꢀ lie in relatively more shielded environments. In the
ꢀꢁ/ꢁꢀ diastereoisomer (12), the opposite chiralities of the
two metal centres are such that only the H6 proton of ring b
lies close to the nitrogen atom of the non-coordinated ring g.
Hence, the downfield signal at 10.00 ppm is attributed to a
single proton. This rationale is based on the assumption that
the non-coordinated pyridine rings of the bridging ligand are
oriented as shown in Diagram 3, which we believe is again
due to the existence of stabilizing C–H · · · N intramolecular
interactions.
Crystal Structures of the Ruthenium Complexes
Crystals of complex (8) were obtained by slow evapora-
tion of a methanol solution of the complex. It crystallizes in
the monoclinic space group P21/n with a full cation (Fig. 1),
two hexafluorophosphate counterions, and two methanol
solvate molecules in the asymmetric unit. The structure
determination confirms the mononuclear nature of (8) and
unambiguously establishes that the ligand chelates to the
ruthenium atom through two geminally substituted pyri-
dine rings (with the formation of a six-membered chelate
ring), rather than through two vicinally related rings (and
a seven-membered chelate ring). As surmised above, the
non-coordinated dipyridylmethyl substituent exists in the
bowsprit position of the chelate ring’s boat conformation. As
shown in Figure 1 the non-coordinated pyridine rings are ide-
ally disposed to coordinate to a second ruthenium centre. The
bonding geometry of the ruthenium atom is unremarkable.
The structure of (10) was also determined by X-ray
crystallography and is shown in Figure 2. It crystal-
¯
lizes in the triclinic space group P1 with a full cation,

Ruthenium(ii)–Di(2-pyridyl)methane Derived Complexes
661
two hexafluorophosphate anions, a methanol, and a water
molecule in the asymmetric unit. The structure and confor-
mation of the complex supports the previously discussed
1H NMR conclusions. The boat conformation of the six-
membered chelate ring destroys the potential C2 symmetry of
the complex.As the structure shows, the strongly shielded H3
proton of one of the non-coordinated rings lies directly over
one of the bpy rings. Conversely, the H3 proton of the other
non-coordinated ring is in a highly deshielded environment,
lying very close to the nitrogen atom of the aforementioned
non-coordinated pyridine ring. The structure also shows that
the two H6 protons of the coordinated pyridine rings of the
tetradentate ligand both lie over a pyridine ring of the ancil-
lary bpy ligands and hence these protons are shielded due to
through-space ring anisotropy effects. Once again the bond-
ing geometry of the ruthenium atom is normal. The most
closely related literature structure is that of the Ru(bpy)2
complex of 1,1-di(1-methylimidazol-2-yl)ethene and this has
similar bonding geometry about the ruthenium atom and a
similar conformation of the six-membered chelate ring.[16]
Absorption Spectra and Redox Properties
Table 2 lists the electronic absorption maxima and redox
potentials recorded in acetonitrile solutions for the complexes
(6)–(13).The red mononuclear complexes (6)–(11) all exhibit
a lowest energy MLCT absorption at a similar wavelength
to that of [Ru(bpy)3]2+ (452 nm).[5a] However, the redox
potentials reveal that the Ru(bpy)2 complexes (6) and (8)
of the non-conjugated ligands (1) and (2) are slightly easier
Fig. 1. A perspective view of the structure of complex (8). Hexa-
fluorophosphate counterions and methanol solvate molecules are not
shown. Selected bond lengths [Å] and angles [◦]: Ru(1)–N(61) 2.046(4),
Ru(1)–N(51) 2.058(4), Ru(1)–N(71) 2.059(4), Ru(1)–N(81) 2.075(4),
Ru(1)–N(21) 2.124(4), Ru(1)–N(11) 2.135(4), N(61)–Ru(1)–N(51)
79.5(2), N(61)–Ru(1)–N(71) 87.1(2), N(51)–Ru(1)–N(71) 95.9(2),
N(61)–Ru(1)–N(81) 92.3(2), N(51)–Ru(1)–N(81) 170.4(2), N(71)–
Ru(1)–N(81) 78.7(2), N(61)–Ru(1)–N(21) 94.4(2), N(51)–Ru(1)–
N(21) 85.7(2), N(71)–Ru(1)–N(21) 178.0(2), N(81)–Ru(1)–N(21)
99.9(2), N(61)–Ru(1)–N(11) 171.7(2), N(51)–Ru(1)–N(11) 92.7(2),
N(71)–Ru(1)–N(11) 91.1(2), N(81)–Ru(1)–N(11) 95.3(2), N(21)–
Ru(1)–N(11) 87.7(2).
Fig. 2. A perspective view of the structure of complex (10). Counter-
ions and solvate molecules are not shown. Selected bond lengths [Å] and
angles [◦]: Ru(1)–N(61) 2.049(5), Ru(1)–N(71) 2.053(7), Ru(1)–N(81)
2.063(6), Ru(1)–N(51) 2.078(6), Ru(1)–N(21) 2.111(6), Ru(1)–N(11)
2.116(5), N(61)–Ru(1)–N(71) 90.9(2), N(61)–Ru(1)–N(81) 95.4(2),
N(71)–Ru(1)–N(81) 77.7(3), N(61)–Ru(1)–N(51) 78.8(2), N(71)–
Ru(1)–N(51) 96.5(3), N(81)–Ru(1)–N(51) 171.8(2), N(61)–Ru(1)–
N(21) 92.7(2), N(71)–Ru(1)–N(21) 175.8(2), N(81)–Ru(1)–N(21)
99.8(2), N(51)–Ru(1)–N(21) 86.3(2), N(61)–Ru(1)–N(11) 175.6(3),
N(71)–Ru(1)–N(11) 89.8(2), N(81)–Ru(1)–N(11) 89.0(2), N(51)–
Ru(1)–N(11) 96.8(2), N(21)–Ru(1)–N(11) 86.7(2).
Table 2. Visible absorption maxima and redox potentials for complexes (6)–(13)
λ (nm)A,B
Eox
Ered(1)
Ered(2)
Ered(3)
Ered(4)
Ered(5)
C,D
C,D
C,D
C,D
C,D
C,D
(6)
(7)
(8)
434(sh), 451
434, 452(sh)
433, 455
436, 455
454
456
452, 632
453, 628
+1.19
−1.45
−1.64
−1.86
−1.95
+1.09
−1.54E
−1.45
−1.71
+1.20
−1.67
(9)
+1.09
−1.54
−1.73
(10)
(11)
(12)
(13)
+1.17
−1.25
−1.60
−1.86
+1.07
−1.33E
−0.30(1e−)
−0.43(1e−)
−1.68
−1.93
+1.24(2e−)
−0.77(1e−)
−1.51(2e−)
−1.80(2e−)
−2.20(2e−)
−2.08(2e−)
−2.38(2e−)
+1.25(2e−)
−0.80(1e−)
−1.53(2e−)
A The MLCT band measured in CH3CN ( 2 nm).
B sh = shoulder.
C Potentials quoted in V versus SCE in CH3CN/0.1 mol L−1 [(n-C4H9)4]PF6 (the ferrocene/ferrocenium couple
occurred at +310 mV versus SCE).
D Uncertainty in E1/2 values approximately 0.01V.
E Irreversible (approximate value estimated from anodic half-scan).

662
P. J. Steel et al.
to oxidize and more difficult to reduce than [Ru(bpy)3]2+
(+1.26, −1.33V).[5a] On this basis, we believe that these lig-
ands provide less π-backbonding stabilization than bpy. In
contrast, the mononuclear complexes of the conjugated lig-
and(3)undergoreductionatalowerpotential. Fortheseriesof
mononuclear complexes the redox potentials of the Me2bpy
complexes are shifted by about 100 mV related to those of
the analogous bpy complexes, consistent with the known[17]
electron-donating effect of around 25 mV per methyl group.
The green dinuclear complexes (12) and (13) also exhibit
MLCT visible absorption maxima associated with the bpy
ligands at approximately 452 nm. However, the lowest energy
transitions occur near 630 nm and correspond to electron
transfer into the bridging radialene ligand. Both diastereoiso-
mersareoxidizedatasimilarpotentialtothatof[Ru(bpy)3]2+
but undergo two sequential one-electron reductions at a
much lower potential, consistent with the fact that the radi-
alene ligand (4) is known to have very low-energy lowest-
and second-lowest unoccupied molecular orbitals (LUMO,
SLUMO).[18] Despite the potential conjugation provided by
this ligand for interaction between the metal centres, the
simultaneous two-electron oxidation event suggests a lack of
communication between ruthenium centres in these dinuclear
complexes.
an Ag/Ag+ (0.1 mol L−1 [(n-C4H9)4N]PF6 in acetonitrile) reference
electrode. Ferrocene was added as an internal standard on comple-
tion of each experiment (the ferrocene/ferrocenium couple occurred
at +310 mV versus SCE). Cyclic voltammetry was performed with a
sweep rate of 100 mV s−1
.
Di(2-pyridyl)ketone (Aldrich), RuCl3 · xH2O (Strem, 99%),
2,2ꢀ-bipyridine (bpy; Aldrich, 99+%), 4,4ꢀ-dimethyl-2,2ꢀ-bipyridine
(Me2bpy; Aldrich, 99%), ammonium hexafluorophosphate (NH4PF6;
Aldrich, 99.99%), tetra-n-butylammonium hexafluorophosphate ([(n-
C4H9)4N]PF6; Fluka, 99+%), ethylene glycol (Ajax), [D3]acetonitrile
(CD3CN; Cambridge Isotope Laboratory, 99.8 atom-% D), and labo-
ratory reagent solvents were used as received. Di(2-pyridyl)methane
(1),[8] 1,1,2,2-tetra(2-pyridyl)ethane (2),[8] hexa(2-pyridyl)[3]radialene
(4),[10] [Ru(bpy)2Cl2],[19] and [Ru(Me2bpy)2Cl2][20] were prepared
according to the literature procedures. Acetonitrile (Aldrich, 99.9+%)
and acetone (BDH, HPLC grade) were distilled under nitrogen from
CaH2 and K2CO3, respectively, immediately prior to use. SP Sephadex
C-25 (Amersham Pharmacia Biotech), SP Sepharose Fast Flow (Amer-
sham Pharmacia Biotech), silica gel 200–400 mesh (Aldrich), and alu-
mina 100–200 mesh were employed for the chromatographic separation
and purification of ruthenium complexes.
1,1,2,2-Tetra(2-pyridyl)ethanol (5)
When di-2-pyridylmethane was stored in a round-bottomed flask, a
colourless solid slowly precipitated out of the oil over a period of weeks.
By dissolving the oil in ether and collecting the insoluble solid, 1,1,2,2-
tetra(2-pyridyl)ethanol, was obtained. mp 161–164◦C. Anal. calc. for
3
C22H18N4O · /4H2O C 71.82, H 5.34, N 15.23%; found C 71.84, H
5.08, N 15.23%. δH (CDCl3) 8.45 (2 H, d, H6), 8.34 (2 H, d, H6), 8.24
(1 H, bs, OH), 7.79 (2 H, d, H3), 7.43 (6 H, m), 6.92 (4 H, m), 6.29 (1 H,
s, CH). δC (CDCl3) 163.6, 160.4, 148.0, 147.8, 136.0, 135.8, 125.3,
121.2, 121.1, 121.1, 82.47, 59.49.
Conclusion
Ruthenium-bis(bpy) and -bis(Me2bpy) complexes of the
model ligand di(2-pyridyl)methane (1) and its derived
multidentate derivatives (2)–(4) have been prepared and
characterized by NMR, absorption spectroscopy, electro-
chemical measurements, and, in two cases, by X-ray crystal-
lography. Complexes of (2) and (3) exist as conformationally
rigid species with lower than expected symmetry. Ligands
(2) and (3) proved surprisingly resistant to forming dinuclear
ruthenium complexes. The two diastereoisomeric dinuclear
complexes of (4), ꢀꢁ/ꢁꢀ and ꢀꢀ/ꢁꢁ (rac), are shown
to be locked in conformations of C1 and C2 point-group
symmetry, respectively.This represents a rare example where
the ꢀꢁ/ꢁꢀ-dinuclear complex of a achiral, symmetrically
bridging ligand is not a meso-compound.
Tetra(2-pyridyl)ethylene (3)
Method A: Compound (2) (220 mg, 0.65 mmol) and DDQ (190 mg,
0.85 mmol) were dissolved in 30 mL of dry toluene and refluxed for
three hours with monitoring of the reaction by TLC and NMR. The
solution was filtered, the residue washed with toluene (2 × 5 mL), and
the toluene removed in vacuo. The residue was dissolved in CHCl3
(50 mL) and washed with 50 mL of 1M NaOH solution followed by
50 mL of water, and then dried over anhydrous sodium sulfate. After
removal of the solvent the products were purified on silica gel, eluting
with 10% methanol/chloroform to give recovered (2) (41 mg, 19%) and
(3) (55 mg, 25%). Di-2-pyridylketone is also formed in the reaction but
this was not recovered.
Method B: The alcohol (5) (160 mg, 0.45 mmol) was dissolved in
pyridine (10 mL) and cooled to −10◦C. Thionyl chloride (1 mL) was
added slowly to give a yellow solution that went red then brown over the
next 3 h. Water was cautiously added to the reaction mixture, which
was then made alkaline with potassium carbonate. Extraction with
dichloromethane (3 × 50 mL) gave a pale brown extract that was dried
over anhydrous sodium sulfate and the solvent removed in vacuo. The
resultant oily brown solid was triturated with ether and then recrystal-
lized from ether to give (3) (123 mg, 81%). mp 178–180◦C (dec.). Anal.
Experimental
Instrumentation and Materials
1H NMR, 1-D TOCSY, 1-D NOESY, and 1H–1H COSY experiments
were performed on a Varian Mercury 300 MHz or a Varian 500 MHz
NMR spectrometer at room temperature with CD3CN solutions. The
1H NMR assignments for the compounds are denoted with primes to
indicate the different rings of the multidentate ligands and with letters
to distinguish the bipyridine rings. Electrospray mass spectrometry
(ESMS) was performed on a Micromass LCT-TOF mass spectrometer.
The elemental analyses were performed at the Campbell Microanalyti-
cal Laboratory at the University of Otago. Melting points were recorded
on an Electrothermal melting point apparatus and are uncorrected. Elec-
tronic spectra were recorded in CH3CN using a CARY 5E UV/vis/NIR
or a GBC 920 UV/visible spectrometer.
Electrochemical measurements were performed under argon using
a Bioanalytical Systems BAS 100A Electrochemical Analyzer. Cyclic
and differential pulse voltammograms were recorded in acetonitrile/
0.1 mol L−1 [(n-C4H9)4N]PF6 solution using a glassy carbon or plat-
inum button working electrode, a platinum wire auxiliary electrode, and
1
calc. for C22H16N4 · /2H2O C 76.5, H 4.96, N 16.2; found C 77.1, H
5.32, N 16.2%. HRMS calc. for C22H16N4 336.1375; found 336.1348.
δH (CDCl3) 8.48 (4 H, d, H6ꢀ), 7.39 (4 H, t, H4ꢀ), 7.07 (4 H, d, H3ꢀ), 7.03
(4 H, dd, H5ꢀ). δC (CDCl3) 159.8, 149.3, 144.1, 135.7, 126.4, 121.8.
Complex (6)
[Ru(bpy)2Cl2] (77 mg, 0.16 mmol) and (1) (31 mg, 0.18 mmol) were
refluxed in degassed 3 : 1 ethanol/water (16 mL) for 36 h.This was taken
to dryness in vacuo, redissolved in water, filtered, and the complex
precipitated with an excess of ammonium hexafluorophosphate. The
orange precipitate was recrystallized from methanol to give a dark
red solid. Yield 69 mg (49%). mp 207–209◦C. Anal. calc. for
C31H26N6F12P2Ru C 42.6, H 3.00, N 9.6; found C 42.7, H 3.23, N
9.5%. δH (CD3CN) 8.58 (2 H, d, H3A), 8.49 (2 H, d, H3B), 8.24 (2 H, d,
H6A), 8.20 (2 H, t, H4A), 8.03 (2 H, t, H4B), 7.90 (2 H, t, H4), 7.75–7.69

Ruthenium(ii)–Di(2-pyridyl)methane Derived Complexes
663
(4 H, m, H3, H6B), 7.61–7.56 (4 H, m, H5A, H6), 7.39 (2 H, t, H5B),
7.14 (2 H, t, H5), 4.61 (2 H, s, CH2).
at reflux in a modified microwave oven (Sharp Model R-2V55; 600W,
2450 MHz) on high power for 45 min. Upon cooling, the resultant
red/brown solution was diluted with distilled water (10 mL) and loaded
onto a column (approximately 15 cm long × 2 cm in diameter) of SP
Sepharose Fast Flow cation exchanger. Separation of the mononuclear
and dinuclear products from the crude mixture was achieved via a gradi-
ent elution procedure using aqueous 0.1–0.5 mol L−1 NaCl as the eluent.
Three bands were subsequently eluted: Band 1 (dark purple, 0.1 mol L−1
NaCl), Band 2 (orange, 0.2 mol L−1 NaCl), and Band 3 (brown, 0.4 mol
L−1 NaCl). On addition of a saturated solution of aqueous KPF6 to
each band, the products were extracted into dichloromethane and the
solvent removed in vacuo. The solid residues were dissolved in a min-
imum volume of acetone and loaded onto a short column of silica gel
(2 cm × 2 cm), washed with acetone, water, and acetone, and then eluted
with acetone containing 5% NH4PF6. Addition of water and removal of
the acetone under reduced pressure afforded the pure products. Yield
(Band 2 = (10)), 10.5 mg (52%). mp 180–184◦C (dec.). Anal. calc. for
C42H32N8F12P2Ru C 48.5, H 3.10, N 10.8; found C 48.3, H 3.06, N
10.6%. HRMS calc. for C42H32N8F6PRu 895.1435, found 895.1463.
δH (CD3CN) 10.43 1 H, d, H6A), 8.74 (1 H, d, H3C), 8.67 (1 H, d, H3D),
8.52 (1 H, d, H6), 8.48–8.44 (2 H, m, H3A, H6ꢀ), 8.40 (1 H, d, H3B),
8.31 (1 H, d, H3ꢀ), 8.21 (1 H, t, H4C), 8.09 (1 H, t, H4D), 8.06–8.01
(3 H, m, H6D, H4B, H6ꢀꢀꢀ), 8.01–7.94 (2 H, m, H4A, H4ꢀ), 7.63 (1 H, d,
H6B), 7.57–7.49 (3 H, m, H6C, H4ꢀꢀ, H4ꢀꢀꢀ), 7.47–7.38 (4 H, m, H5B,
H5C, H5D, H5ꢀ), 7.36–7.27 (4 H, m, H5A, H4, H3ꢀꢀ, H3ꢀꢀꢀ), 7.20–7.14
(3 H, m, H5, H6ꢀꢀ, H5ꢀꢀꢀ), 6.88 (1 H, t, H5ꢀꢀ), 5.56 (1 H, d, H3).
Complex (7)
[Ru(Me2bpy)2Cl2] (131 mg, 0.24 mmol) and (1) (42 mg, 0.25 mmol)
were refluxed in degassed 3 : 1 ethanol/water solution (16 mL) for 36 h.
The solution was taken to dryness in vacuo, redissolved in water,
filtered, and the complex precipitated with an excess of ammonium
hexafluorophosphate. The precipitate was purified on alumina with 1 : 9
methanol/dichloromethane.Yield 137 mg (61%). mp 203–206◦C. Anal.
calc. for C31H26N6F12P2Ru C 45.2, H 3.69, N 9.0; found C 45.2, H
3.95, N 9.0%. δH (CD3CN) 8.44 (2 H, s, H3A), 8.35 (2 H, s, H3B), 8.06
(2 H, d, H6A), 7.88 (2 H, t, H4), 7.69 (2 H, d, H3), 7.60 (2 H, d, H6),
7.54 (2 H, d, H6B), 7.41 (2 H, d, H5A), 7.24 (2 H, d, H5B), 7.13 (2 H, t,
H5), 4.60 (2 H, s, CH2), 2.66 (6 H, s, CH3A), 2.54 (6 H, s, CH3B).
Complex (8)
Ligand (2) (21.8 mg, 0.06 mmol) and [Ru(bpy)2Cl2] (63.0 mg,
0.13 mmol) were refluxed in 3 : 1 ethanol/water for 48 h. After cooling
the solvent was removed in vacuo and the residue dissolved in water and
filtered. The resulting red solution was treated with an excess of ammo-
nium hexafluorophosphate to give a red/orange precipitate. The solid
was chromatographed on alumina with a 10% solution of methanol in
dichloromethane. The bright red band was recrystallized from methanol
to give red crystals. Yield 47 mg (75%). mp 237–239◦C. Anal. calc. for
C42H34N8F12P2Ru C 48.4, H 3.29, N 10.8; found C 48.4, H 3.35, N
10.9%. HRMS calc. for C42H34N8F6PRu 897.1592, found 897.1586.
δH (CD3CN) 10.27 (1 H, d, H6A), 8.72 (1 H, d, H3B), 8.68 (1 H, d, H3C),
8.59 (1 H, d, H6), 8.53 (1 H, d, H3A), 8.40 (1 H, d, H3D), 8.28 (1 H, t,
H4A), 8.21 (1 H, d, H6C), 8.17 (1 H, t, H4B), 8.09 (1 H, t, H4C), 8.03
(1 H, t, H4D), 7.95 (1 H, t, H5A), 7.91 (1 H, d, H6ꢀꢀ), 7.88 (1 H, d, H6ꢀ),
7.83 (1 H, m, H4), 7.81 (1 H, m, H3), 7.72 (1 H, t, H4ꢀꢀ), 7.74–7.65 (2 H,
m, H3ꢀꢀ, H6D), 7.56–7.52 (2 H, m, H4ꢀ, H4ꢀꢀꢀ), 7.50–7.42 (3 H, m, H3ꢀꢀꢀ,
H5D, H5C), 7.35–7.30 (2 H, m, H5B, H3ꢀ), 7.20 (1 H, t, H5), 7.15–7.10
(2 H, m, H6ꢀꢀꢀ, H5ꢀꢀ), 6.97 (1 H, dd, H5ꢀ), 6.91 (1 H, d, H6B), 6.75 (1 H,
t, H5ꢀꢀꢀ), 6.71 (1 H, d, CH), 5.90 (1 H, d, CH).
Complex (11)
Ligand (3) (11.0 mg, 0.033 mmol) and [Ru(Me2bpy)2Cl2] (38.1 mg,
0.070 mmol) were refluxed in 3 : 1 ethanol/water for 48 h. After cooling
the solvent was removed in vacuo and the residue dissolved in water
and filtered. The resulting red solution was treated with an excess of
ammonium hexafluorophosphate to give a red precipitate.The solid was
purified on alumina with 1 : 19 solution of methanol/dichloromethane
to give a red solid.Yield 25.6 mg (71%). mp 211–214◦C. Anal. calc. for
C46H40N8F12P2Ru C 50.4, H 3.68, N 10.2; found C 50.1, H 3.69, N
10.3%. HRMS calc. for C46H42N8F6PRu 951.2061, found 951.2044.
δH (CD3CN) 10.26 (1 H, d, H6C), 8.60 (1 H, s, H3A), 8.56 (1 H, d, H6),
8.54 (1 H, s, H3B), 8.45 (1 H, d, H6ꢀ), 8.34 (1 H, d, H3ꢀ), 8.31 (1 H, s,
H3C), 8.25 (1 H, s, H3D), 8.02 (1 H, d, H6ꢀꢀꢀ), 7.96 (1 H, t, H4ꢀ), 7.85
(1 H, d, H6B), 7.53 (1 H, t, H4ꢀꢀꢀ), 7.48 (1 H, t, H4ꢀꢀ), 7.45 (1 H, d, H6D),
7.40–7.36 (2 H, m, H6A, H5ꢀ), 7.31–7.23 (6 H, m, H5A, H5B, H5D,
H4, H3ꢀꢀꢀ, H3ꢀꢀ), 7.19–7.13 (4 H, m, H5C, H5, H5ꢀꢀꢀ, H6ꢀꢀ), 6.87 (1 H, t,
H5ꢀꢀ), 5.51 (1 H, d, H3), 2.66 (3 H, s, CH3A), 2.58 (3 H, s, CH3B), 2.54
(3 H, s, CH3D), 2.43 (3 H, s, CH3C).
Complex (9)
Ligand (2) (20.1 mg, 0.059 mmol) and [Ru(Me2bpy)2Cl2] (67.0 mg,
0.124 mmol) were refluxed in 3 : 1 ethanol/water for 48 h.After cooling,
the solvent was removed in vacuo and the residue dissolved in water
and filtered. The resulting red solution was treated with an excess of
ammonium hexafluorophosphate to give a red precipitate.The solid was
purified on alumina with 1 : 9 solution of methanol/dichloromethane to
give a black solid.Yield 36.7 mg (57%). mp 235–238◦C. Anal. calc. for
C46H42N8F12P2Ru·H2O C 49.5, H 3.97, N 10.0; found C 49.3, H 3.89,
N 9.8%. HRMS calc. for C46H42N8F6PRu 953.2218; found 953.2248.
δH (CD3CN) 10.06 (1 H, d, H6A), 8.59 (1 H, d, H6), 8.56 (1 H, s, H3C),
8.52 (1 H, s, H3D), 8.39 (1 H, s, H3A), 8.25 (1 H, s, H3B), 7.97 (1 H, d,
H6D), 7.93–7.88 (2 H, m, H6ꢀ, H6ꢀꢀ), 7.82–7.76 (3 H, m, H5A, H4, H3),
7.70–7.63 (2 H, m, H4ꢀꢀ, H3ꢀꢀ), 7.55–7.50 (2 H, m, H4ꢀ, H4ꢀꢀꢀ), 7.47–7.43
(2 H, m, H6B, H3ꢀꢀꢀ), 7.29–7.25 (3 H, m, H5D, H5B, H3ꢀ), 7.21 (1 H, t,
H5ꢀ), 7.15–7.07 (3 H, m, H5C, H5ꢀꢀ, H6ꢀꢀꢀ), 6.98 (1 H, dd, H5ꢀ), 6.75–
6.71 (2 H, m, H6C, H5ꢀꢀꢀ), 6.67 (1 H, d, CH), 5.89 (1 H, d, CH), 2.71
(3 H, s, CH3A), 2.62 (3 H, s, CH3C), 2.58 (3 H, s, CH3D), 2.53 (3 H, s,
CH3B).
Complexes (12) and (13)
A suspension of [Ru(bpy)2Cl2] (19.3 mg, 0.0370 mmol) and ligand
(4) (5.0 mg, 0.00925 mmol) in ethylene glycol (0.5 mL) was heated at
reflux in a modified microwave oven (Sharp Model R-2V55; 600W,
2450 MHz) on high power for 25 min. Upon cooling, the resultant
green/brown solution was diluted with distilled water (10 mL) and
loaded onto a column (approximately 15 cm long × 2 cm in diameter)
of SP Sepharose Fast Flow cation exchanger. Separation of the mononu-
clear and dinuclear products from the crude mixture was achieved via a
gradient elution procedure using aqueous 0.1–0.5 mol L−1 N−aC1 l as the
eluent. Four bands were eluted: Band 1 (light red, 0.2 mol L NaCl),
Band 2 (purple, 0.3 mol L−1 NaCl), Band 3 (green, 0.4 mol L−1 NaCl),
and Band 4 (green, 0.4 mol L−1 NaCl). On addition of a saturated solu-
tion of aqueous KPF6 to each band, the products were extracted into
dichloromethane and the solvent removed in vacuo. The solid residues
were dissolved in a minimum volume of acetone and loaded onto a
short column of silica gel (2 cm × 2 cm), washed with acetone, water,
and acetone, and then eluted with acetone containing 5% NH4PF6.
Addition of water and removal of the acetone under reduced pressure
afforded the pure products. The electronic absorption spectra of the
four bands in CH3CN permitted the identification of Band 2 as unre-
acted [Ru(bpy)2Cl2] precursor, while the composition of Bands 1, 3,
and 4 were established by electrospray mass spectrometry. Analysis of
Complex (10)
Method A: Compound (3) (10.9 mg, 0.032 mmol) and [Ru(bpy)2Cl2]
(33.6 mg, 0.069 mmol) were refluxed in 3 : 1 ethanol/water for 48 h.
Silver nitrate was added to remove the chloride anions. After cool-
ing, the solvent was removed in vacuo and the residue redissolved
in water and filtered. The resulting red solution was treated with an
excess of ammonium hexafluorophosphate to give a red/orange precip-
itate. The solid was chromatographed on alumina with a 1 : 9 solution
of methanol/dichloromethane. The bright red band was recrystallized
from methanol to give red crystals. Yield 22.9 mg (69%).
Method B: A suspension of [Ru(bpy)2Cl2](40.2 mg, 0.0773 mmol)
and (3) (6.5 mg, 0.0193 mmol) in ethylene glycol (0.5 mL) was heated

664
P. J. Steel et al.
Table 3. Experimental details for the X-ray crystal structures of
(8) and (10)
SMART CCD area detector, using graphite monochromatized MoKα
radiation (λ 0.71073 Å). Almost complete spheres of data were col-
lected.The structures were solved by direct methods using SHELXS,[21]
and refined on F2 using all data by full-matrix least-squares proce-
dures with SHELXL-97.[22] Hydrogen atoms were included in calcu-
lated positions with isotropic displacement parameters 1.3 times the
isotropic equivalent of their carrier atoms. The function minimized
was ꢂw(Fo2 − Fc2)2, with w = [σ2(Fo2) + (aP)2 + bP]–1, where P =
[max(Fo,0)2 + 2Fc2]/3. Crystallographic data, as CIF files, have been
deposited with the Cambridge Crystallographic Data Centre (CCDC No
200825 & 200826). Copies can be obtained free of charge from: The
Director, CCDC, 12 Union Road, Cambridge CB2 1EZ, U. K. (e-mail:
deposit@ccdc.cam.ac.uk).
Compound
(8)
(10)
Empirical formula
Formula weight
Temperature (K)
Crystal system
Space group
Cell dimensions:
a [Å]
C44H42F12N8O2P2Ru
1105.87
168(2)
Monoclinic
P21/n
C
43H37F12N8O1.50P2Ru
1080.82
168(2)
Triclinic
¯
P1
8.995(3)
24.352(11)
21.704(11)
90
100.89(2)
90
9.361(5)
9.996(5)
24.314(13)
100.296(7)
93.188(8)
91.266(8)
2234(2)
2
b [Å]
c [Å]
α [◦]
β [◦]
γ [◦]
Acknowledgment
Volume [Å3]
Z
4668(4)
4
We thank the Royal Society of New Zealand Marsden Fund
and the Australian Research Council for generous finan-
cial support, and Bruce Clark for the mass spectrometry
measurements.
Density
1.573
1.607
(calculated) [Mg m−3
Absorption
]
0.500
0.519
coefficient [mm−1
F(000)
]
2240
1090
Crystal size [mm3]
θ-range for
0.45 × 0.27 × 0.23
0.57 × 0.25 × 0.02
References
1.93–25.00
2.18–25.00
data collection [◦]
Reflections
[1] F. Blau, Chem. Ber. 1888, 21, 1077.
[2] E. C. Constable, Adv. Inorg. Chem. 1989, 34, 1.
[3] C. Kaes, A. Katz, M. W. Hosseini, Chem. Rev. 2000, 100, 3553.
[4] (a) F. R. Keene, Coord. Chem. Rev. 1997, 166, 122. (b)
F. R. Keene, Chem. Soc. Rev. 1998, 27, 185.
[5] (a) A. Juris, V. Balzani, F. Barigelletti, S. Campagna, P.
Belser, A. von Zelewsky, Coord. Chem. Rev. 1988, 84, 85. (b)
V. Balzani, A. Juris, M. Venturi, S. Campagna, S. Serroni, Chem.
Rev. 1996, 96, 759.
Collected
54 409
15 868
Independent Rint
8205 0.0507
6719
8205/12/653
7771 0.0663
3322
7771/0/616
Observed [I > 2σ(I)]
Data/restraints/
parameters
R1[I > 2σ(I)]
0.0675
0.1935
0.0638
0.1556
wR2 (all data)
[6] C. Richardson, P. J. Steel, D. M. D’Alessandro, P. C. Junk,
F. R. Keene, J. Chem. Soc., Dalton Trans., 2002, 2775, and
references therein.
Band 1 revealed the presence of two mononuclear ruthenium species:
a major species, [Ru(bpy)2(L)]2+ where L = di-2-pyridylketone, and a
minor species, where L = di-2- pyridylketone ethylene acetyl. Bands 3
and 4 were identified as the diastereoisomeric forms of [{Ru(bpy)2}2
(µ-4)](PF6)4. Yields: Band 3 = (12), 3.5 mg (19%); Band 4 = (13),
3.2 mg (18%).
[7] E. C. Constable, P. J. Steel, Coord. Chem. Rev. 1989, 93, 205.
[8] A. J. Canty, N. J. Minchin, Aust. J. Chem. 1986, 39, 1063.
[9] (a) A. J. Canty, N. Chaichit, B. M. Gatehouse, E. E. George,
G. Hayhurst, Inorg. Chem. 1981, 20, 2414. (b) M. Rosenblum,
M. M. Turnball, B. M. Foxman, Organometallics 1986, 5, 1063.
(c) E. Spodine, J. Manzur, M. T. Garland, J. P. Fackler, Jr., R. J.
Staples, B. Trzcinska-Bancroft, Inorg. Chim. Acta 1993, 203, 73.
[10] (a) P. J. Steel, C. J. Sumby, Chem. Commun. 2002, 322. (b)
P. J. Steel, C. J. Sumby, Inorg. Chem. Commun. 2002, 5, 323.
[11] L. J. Henderson, M. Ollino, V. K. Gupta, G. R. Newkome,
W. R. Cherry, J. Photochem. 1985, 31, 199.
[12] A. J. Canty, N. J. Minchin, Inorg. Chim. Acta 1985, 100, L13.
[13] (a) P. J. Steel, F. Lahousse, D. Lerner, C. Marzin, Inorg. Chem.
1983, 22, 1488. (b) P. J. Steel, E. C. Constable, J. Chem.
Soc., Dalton Trans. 1990, 1389. (c) A. J. Downard, P. J. Steel,
J. Steenwijk, Aust. J. Chem. 1995, 48, 1625. (d) I. G. Phillips,
P. J. Steel, Aust. J. Chem. 1998, 51, 371.
[14] (a) T. Steiner, Angew. Chem. Int. Ed. 2002, 41, 48. (b)
C. B. Aakeröy, A. M. Beatty, Aust. J. Chem. 2001, 54, 409.
[15] H. Hopf, G. Maas, Angew. Chem. Int. Ed. Engl. 1992, 31, 931.
[16] A. J. Canty, P. R. Traill, B. W. Skelton, A. H. White, Inorg.
Chim. Acta 1997, 255, 117.
[17] D. L. Jameson, J. K. Blaho, K. T. Kruger, K. A. Goldsby, Inorg.
Chem. 1989, 28, 4312.
[18] K. Matsumoto, Y. Harada, T. Kawase, M. Oda, Chem. Commun.
2002, 324.
(12): ESMS 829.1 (24%, Ru2(4)(PF6)22+), 504.4 (100%, Ru2(4)-
(PF6)3+), 342.0 (73%, Ru2(4)4+). δH (CD3CN) 10.00 (1 H, d, H6A),
8.93 (1 H, d, H3B), 8.85 (1 H, d, H3C), 8.78 (2 H, m, H6), 8.71 (1 H, d,
H3D), 8.54 (2 H, m, H3B, H3F), 8.38 (1 H, d, H3E), 8.34–8.10 (10 H,
m, H3A, H4B, H4C, H4D, H4F, H4G, H4H, H6D, H6H, H6ꢀ), 8.07
(1 H, t, H4E), 7.98 (1 H, d, H6C), 7.88–7.82 (3 H, m, H6G, H4, H6ꢀꢀꢀ),
7.80 (1 H, t, H4A), 7.76–7.66 (4 H, m, H5B, H3E, H3F, H6), 7.64
(1 H, t, H5A), 7.58 (1 H, t, H5C), 7.55–7.40 (7 H, m, H5D, H5E, H5F,
H5G, H5H, H3, H4ꢀ), 7.31 (1 H, dd, H5), 7.25 (1 H, t, H5ꢀ), 7.17 (1 H,
d, H6ꢀꢀꢀꢀ), 7.15 (1 H, d, H6ꢀꢀ), 7.13–7.06 (2 H, m, H3ꢀ), 7.05 (1 H, t,
H5ꢀꢀꢀ), 7.00 (1 H, d, H3ꢀꢀꢀꢀ), 6.99 (1 H, t, H5ꢀꢀꢀꢀ), 6.89–6.84 (2 H, m, H4ꢀꢀꢀ,
H4ꢀꢀꢀꢀ), 6.70 (1 H, t, H5ꢀꢀ), 6.54 (1 H, d, H3ꢀꢀꢀ), 6.37 (1 H, t, H4ꢀꢀ), 4.93
(1 H, d, H3ꢀꢀ).
(13): ESMS 829.1 (43%, Ru2(4)(PF6)22+), 504.4 (100%, Ru2(4)
(PF6)3+), 342.0 (42%, Ru2(4)4+). δH (CD3CN) 9.73 (2 H, d, H6A),
8.81 (2 H, d, H3C), 8.73 (2 H, d, H3D), 8.43 (2 H, d, H3B), 8.40 (2 H,
d, H3A), 8.28 (2 H, d, H4C), 8.16–8.13 (4 H, m, H4D, H6D), 8.08 (2 H,
t, H4B), 7.96 (4 H, m, H4A, H4ꢀꢀ), 7.91 (6 H, m, H6C, H6, H6ꢀꢀ), 7.75–
7.65 (6 H, m, H5A, H6B, H3ꢀꢀ), 7.51 (4 H, m, H5B, H5C), 7.47 (2 H, t,
H5D), 7.38 (2 H, t, H5ꢀꢀ), 7.13 (2 H, d, H6ꢀ), 6.95 (2 H, t, H5ꢀ), 6.90–6.83
(6 H, m, H3ꢀ, H4ꢀ, H5), 6.27 (2 H, t, H4), 4.69 (2 H, d, H3).
[19] B. P. Sullivan, G. J. Salmon, T. J. Meyer, Inorg. Chem. 1978,
17, 3334.
[20] P. A. Mabrouk, M. S. Wrighton, Inorg. Chem. 1986, 25, 526.
[21] G. M. Sheldrick, Acta Crystallogr., Sect. A 1990, 46, 467.
[22] G. M. Sheldrick, SHELXL-97 1997 (University of Göttingen:
Göttingen).
X-Ray Crystallography
Crystal data and experimental details of the data collections and struc-
ture refinements are listed inTable 3. Data were collected with a Siemens